The present invention relates to an optical data recording and reproducing apparatus, or more in particular, to the diagnosis of the erase function of an apparatus for recording and reproducing data on an optical disk.
FIG. 3 shows a phase change between an amorphous state A and crystal state C of a phase-change recording medium of a conventional optical data recording and reproducing apparatus. The reflectivity in amorphous state A is smaller than that in crystal state C.
When a part of the recording medium is increased to a temperature near the melting point and annealed, a crystal state is obtained. When the part in crystal state C is locally increased in temperature to a level near the melting point followed by quenching, in contrast, the amorphous state A is attained.
FIG. 4(a) shows a configuration of a light beam for realizing conditions for temperature increase followed by quenching and temperature increase by annealing of the recording medium, and FIG. 4(b) a light distribution therefor. In FIG. 4, reference numeral 13 designates a guide track deposited with a recording layer by evaporation, numeral 14 an identifier (ID field) for a sector including such data as track address and sector address, numeral 15 a data field for recording data, numerals 16a, 16b gaps for absorbing time variations due to rotational variations of the disk, numeral 17 a recording and reproducing light beam in short diameter, numeral 19 a light intensity distribution thereof, numeral 18 an erase light beam in long diameter, and numeral 20 a light intensity distribution thereof. Two light beams, by creating annealing conditions with long diameter and quenching conditions with short diameter, perform the erasing and recording operations in one revolution of the disk, thus making what is called simultaneous erasing possible. FIG. 4(c) shows a waveform of a reproduction signal produced from the sector identifier (ID field) 14, data field 15, gap 16a, 16b formed on the guide track of the optical disk, with the reflectivity of the sector identifier (ID field) 14, gap 16a, 16b and data field 15 decreasing in that order.
FIG. 4(d) shows a write gate signal 102 for commanding the writing of the recording-reproducing light beam 17 set in a record mode and modulated with the write data, in the data field 15. FIG. 4(e) shows an erase gate signal 103 for controlling the time during which the erase light beam 18 is irradiated on the data field 15 of the guide track 13 with a predetermined intensity. Data is recorded in the data field 15 with the succeeding recording-reproducing light beam 17 while erasing the data field 15 with the preceding erase light beam 18 by enabling the write gate signal 102 and the erase gate signal 103. At the end of data recording, the write gate signal 102 and the erase gate signal 103 are both turned off.
In the above-mentioned configuration, however, the erase light beam 18 and the recording-reproducing light beam 17 are exactly aligned on the same guide track, and therefore it is necessary both to trace the guide track 13 with high accuracy and to irradiate the erase light beam 18 and the recording-reproducing light beam 17 on a sector to be erased with a predetermined erasing power and recording power respectively. For simultaneous erasing, it is important to determine by prior diagnosis that these operations are performed normally.
Diagnosis of the erase function is performed by rewriting a predetermined data in a predetermined sector and comparing the data read from an optical disc with original write data.
With the increase in the number of erasing and recording processes, the grooves of the guide track of the recording medium are deformed and the recording film is separated from the disk material due to the strain of the heat cycle. This phenomenon is called the fatigue of the recording medium and sharply deteriorates the bit error rate (BER) of the optical disk. Especially, a long burst that results poses the problem of inaccurate self-diagnosis of the erase function making it impossible to determine whether a burst error has been caused by the erasing failure due to an inferior erase function or the deterioration of the recording medium.